The present invention relates to a method of manufacturing a ceramic and, more particularly, to a method of manufacturing a rare earth oxysulfide ceramic.
According to a description of Japanese Patent Disclosure (Kokai) No. 58-204088, a ceramic of a fluorescent material obtained by partially substituting a rare earth oxysulfide (RE.sub.2 O.sub.2 S; RE is a rare earth element) with another rare earth element such as Gd.sub.2 O.sub.2 S:Pr can be used for a scintillation detector. In this case, in order to obtain a large amount of light emission from the ceramic, the ceramic must have small light loss and high light transmittance. In addition, coloration, i.e., light absorption of the ceramic, and light scattering due to pores or segregates inside the ceramic must be suppressed.
A ceramic with less pores and less inclusions is conventionally manufactured by the hot press method or the hot isostatic press method. This is because an additive material may be left as segregates in the pressureless-sintering process when it is used to obtain high-density ceramics.
However, in the hot press method, no shield is present between a ceramic material and ambient atmosphere and the ceramic material tends to be adversely affected by high-temperature atmosphere. Therefore, when a rare earth oxysulfide likely to be decomposed at a high temperature is used as a material, coloration or degradation of emission efficiency of the ceramic occurs upon decomposition.
On the other hand, with the hot isostatic press method in which a material is sealed in an airtight vessel and a hot isostatic press process is performed, the above decomposition does not occur because a shield is present between the material and the atmosphere. However, since the airtight vessel and the ceramic material are in direct contact with each other, coloration tends to occur due to the reaction between the vessel and the material or diffusion of a metal constituting the vessel into the ceramic.